Referring to FIG. 1, housings for mobil power amplifiers, such as those used in automobiles, or the like, typically include a large heat dissipating heat sink 10 forming a top wall 12 and two lateral side walls 14, 16 which extend downwardly from oppositely facing lateral edges of the top wall 12. Lateral foot extensions 18, 20 which form integral portions of the heat sink 10 extend outwardly from the distal lower ends of the lateral side walls 14, 16 and form mounting apertures 22. Oppositely facing heat sink front and back edges 24, 26, respectively, define an open area which allow power, ground, and input and output mechanical hook-ups. Screw holes 31 are provided on both the front and back edges 24, 26. The top member 10 defines two co-planar recesses 28, 30 on facing surfaces of the lateral side walls 14, 16 near the lower distal ends.
In addition, the casing typically includes a base plate 29 received in the recesses 28, 30 to form a casing lower wall, and two oppositely facing front and back plates 32, 34 respectively. Once the base plate 29 is inserted between recesses 28, 30, the front and back plates 32, 34 are securely fastened to the front and back edges 24, 26 respectively via screws 36 extending through plates 32, 34 and into holes 31.
When located for use, the entire housing should be secured to a flat surface to minimize agitation of the amplifier and in particular the amplifier electronics, thus prolonging the amplifiers useful life. When an amplifier is improperly secured, vibration and collision with nearby items can cause serious damage to both the amplifier components and surrounding items.
To properly mount an amplifier, mounting bolts (not shown) extend through mounting apertures 22 and into a flat support surface. The flat surface is usually an electrically conductive surface connected to an automobile chassis so that after mounting, the surface and chassis operate as an amplifier ground.
In addition to acting as a heat sink for dissipating amplifier heat, as a mounting means and as a ground, the above described housing acts as an amplifier protector to eliminate physical contact with amplifier components. The top member 10 is typically formed of an extruded aluminum which can absorb substantial impact. Nevertheless, where impact is sufficient, the amplifier housing can become damaged. Typical housing damage includes marred or even functionally damaged foot extensions 18, 20 resulting from the heat sink 10 moving to absorb impact force. Where an amplifier can be located in a "hidden space", disfiguring housing damage is relatively unimportant. However, where a damaged housing cannot function properly to protect, mount, or dissipate heat, the damaged portion must be replaced.
While the above described amplifier housing and similarly designed housings have been widely used throughout the mobile audio power amplifier industry for many years, the disadvantages associated with such housings have become increasingly important as typical amplifier environments have changed significantly. For example, suitable hidden space within an automobile has becomes less available as more compact automobiles are designed and more existing hidden space is required to house new or improved factory installed option hardware. Even where sufficient hidden space exists, it is often the case that no defining wall surrounding the space forms a completely flat surface large enough to securely support an amplifier. Many times defining walls are curved to conform to the external shape of an automobile or the internal shape of a passenger compartment or are formed with ribs to increase wall strength.
Where suitable hidden space is not available, add on automotive equipment must be located in relatively more suitable and easily observable locations such as the rear section of a utility vehicle, the hatchback of a small car, or the trunk of a sedan. Housing appearance is important where an amplifier is observable when operationally located. When an amplifier is observable, exposed securing screw heads on the front and back plates are undesirable. This is particularly true where an amplifier is located in an automobile and the entire internal environment of the automobile is completely finished which is almost universally the case.
The above described housing configuration offers no way to hide or cover the securing screw heads. Other housing configurations which do hide screw heads are more complex requiring additional specially designed and manufactured components. These specially designed components are relatively expensive and difficult to install.
In addition, while marred housing surfaces may be acceptable when hidden, such disfiguring damage, even where the damage does not affect amplifier performance, is undesirable where the housing is observable within a automobile. Even slightly damaged housings should be replaced. The heat sink 10 is a single integral piece, and therefore where the heat sink 10 is damaged, the entire sink must be replaced. Because the heat sink is a complex extrudate, replacement is typically expensive. Unfortunately it is usually the top heat sink member 10 and lateral foot extensions 18 and 20 which absorb unintended blows and becomes disfigured.
Another problem with the above described housing configuration is that there is no easy way to mitigate ground loop noise. Ground loop noise is caused when two or more points in an electrical system that are nominally at ground potential are connected by a conducting path such that the two points are not at the same ground potential. In an automobile, the automobile chassis is typically connected to battery ground so that, any component connected to the chassis is theoretically connected to a unipotential ground point. In reality, however, because automobile stereo components will typically be connected to ground through special grounding wires which are characterized by different lengths and resistances, in fact, the direct connections to system components may have slightly different potentials. With an amplifier, where the amplifier is grounded through a grounding wire and the conductive housing is also grounded, ground loop potential possibilities exist.
Yet a further problem with the above described configuration is that it provides a transmission path along the bottom plate for transmitting magnetic flux generated by a power transformer which is a standard component in all amplifiers. This can produce unintended signal and system noise as transformer windings cause a current in the bottom plate which produces a magnetic field which in turn alters input signals by slightly changing input currents (through transformer action).
Therefore, it would be advantageous to have a mobile amplifier housing and mounting system which substantially eliminates observable and unfinished screw heads, limits the affects of stray magnetic flux and ground loop noise, minimizes the costs associated with replacing housing and mounting components, and which can be manufactured and installed inexpensively.